The present invention relates generally to fasteners and more particularly to a smart material actuated fastener.
Recently, some researchers have theoretically disclosed the use of shape memory polymers for fasteners. For example, reference should be made to U.S. Patent Publication No. 2010/0154181 entitled “Shape Memory Fastener” published on Jun. 24, 2010, and U.S. Patent Publication No. 2009/0235494 entitled “Active Material Based Fasteners Including Cable Ties and Twist Ties” which published on Sep. 24, 2009, both of which are incorporated by reference herein. It is noteworthy, however, that the fasteners of most of the disclosed concepts are entirely made of the shape memory polymeric material. This is extremely disadvantageous from a practical standpoint due to the very high cost of the shape memory polymers and due to the likely fastening performance degradation thereof.
In accordance with the present invention, a smart material actuated fastener is provided. In another aspect, a fastener includes a shape memory material and a non-shape memory material with the shape memory material being a minority of the total fastener materials. A further aspect provides a fastener having workpiece-engaging surfaces made of an inactive and non-shape memory material. Still another aspect of the present fastener includes legs which are moved in response to an energization change of a shape memory material. In another aspect, at least a portion of a shape memory material is internally located and/or insert molded within an inactive material. Still another aspect employs a fastener assembly with a generally rigid segment having a curved surface or cavity which secures an elongated tube, wire or other component workpiece thereagainst with the assistance of a shape memory material.
The present invention fastener is advantageous over prior devices such that the shape memory material allows for more secure attachment and fastening of the present fastener to the workpiece(s) but without greatly increasing the part expense. Additionally, the present fastener advantageously uses conventional polymeric or metallic materials, which are inactive upon energization, on workpiece-engaging surfaces to obtain the workpiece insertion and extraction forces required but while also providing an actuation force with a shape memory or active material in a portion of the fastener which is not directly interfacing with the workpiece and/or in a location which is more tolerant of the performance characteristics unique to such shape memory materials. Additional advantages and features of the present invention will become apparent from the following description and appended claims taken in conjunction with the accompanying drawings.